This invention relates generally to coupling assemblies and more particularly to coupling assemblies suitable for the field repair of damaged pipes. The invention is especially useful for the repair of fiber reinforced thermosetting resin plastic pipe of the type disclosed in Carter U.S. Pat. Nos. 3,700,519 and 4,053,343 assigned to the same assignee as the present invention.
When pipes carrying gases or liquids are damaged in a field environment, it is generally necessary to have means available for quickly and easily repairing the damaged pipe sections. Usually this is accomplished by cutting the pipe to remove the damaged section and replacing it with a coupling assembly to connect the two ends of the undamaged pipe. Such repairs must provide an effective pressure-tight seal so that the fluid being carried by the pipe does not leak at the junctions of the pipes to the coupling. Furthermore, the coupling must serve to hold the ends of the undamaged pipe in securely coupled relationship when the joint is subjected to forces acting axially, in torque and in bending.
Because of its greater resistance to corrosive fluids and substantial mechanical strength, plastic pipe of the type described in the patents referred to above is being used extensively in the chemical industries. The usual method for joining plastic pipe sections of this type is by cementing. While such technique is acceptable for original installations, it is not convenient for the field repair of damaged pipe sections in an existing installation. Cementing plastic pipe sections requires a certain amount of expertise and special equipment which may not be available in the field. Furthermore, such technique cannot be accomplished rapidly. Accordingly, a number of coupling assemblies for connecting plastic pipe sections in the field have been developed. Such assemblies typically include a sleeve which provides a seal between juxtaposed or abutting pipe sections for containing the fluid flowing therethrough, and clamping means for clamping the pipe sections in coupled relationship to prevent separation of the coupled sections.
Daigle U.S. Pat. No. 4,045,060; Aug. 30, 1977, discloses a pipe coupling assembly which includes a central cylindrical section having internal sealing rings for providing a seal between the central section and abutted pipe sections inserted therein. Split-ring pipe retaining end members are attached to the central section by means of bridging lugs. The split-ring retaining members are provided with apertured flanges so that the rings may be tightened together against the pipe by means of bolts. The inner surfaces of the split-ring retaining members are serrated to provide a secure anchor to the pipe sections being joined.
Fason U.S. Pat. No. 2,570,224; Oct. 9, 1951, discloses a pipe coupling which has a central cylindrical section having internal sealing rings. The outer diameter of each end of the central section is threaded and adapted to receive a nut which is coaxial with the pipe sections. The coupling is anchored to the pipe sections by means of split rings which are compressed between each end of the central coupling sections and the collar on the nuts, when the nuts are tightened on the central section. The split rings are provided with a sharp corner which bites into the pipe sections to hold them in place with the coupler. A coupling of this type requires pipe wrenches able to span the diameter of the central section and the coaxial nuts for its installation.
Wood et al U.S. Pat. No. 4,109,941; Aug. 29, 1978, discloses another coupling assembly for plastic pipes. The assembly includes a sleeve having longitudinally spaced grooves which receive O-ring seals and which is adapted to slip over the ends of juxtaposed pipe sections. Encasing tubing sections are placed around the outer diameter of the sleeve in the area of each O-ring. Split clamping rings with flanges for receiving bolts and joined by spacer bars overlay the central tubing section. The clamping rings connect to the pipe sections entering the coupling and have a plurality of spaced grooves which deform the surface of the pipe when the clamping rings are tightened thereon. This provides an anchor for securing the two pipe sections in the proper coupling relationship. The spacer bars are designed to apply pressure against the encasing tubing surrounding the sleeve. This coupling is overly complicated, requiring the use of separate encasing tubing surrounding the sleeve in order to provide a good seal.
In each of the coupling assemblies described above the clamping means and the sleeve or central section having the sealing means are interconnected. As a result, any mechanical stress imparted to the clamping assembly is transmitted to the sleeve or central cylindrical section, thereby lessening the effectiveness of the sealing means. In fact, the very interaction of the clamping means and the sleeve or central section causes the latter component to be subjected to mechanical stress.
It is desired to provide a coupling assembly having a simple construction, compact size, which requires no special tools to install, and moreover, which has the components of the assembly so constructed and related that the sealing means therof is capable of serving at optimum conditions free of mechanical stresses.